Self-supporting tyre for vehicle wheels, and method of manufacturing the same

ABSTRACT

A self-supporting tyre for vehicle wheels comprises a carcass structure ( 2 ) having at least one carcass ply ( 3   a,    3   b ) provided with end flaps ( 19, 21 ) in engagement with respective annular reinforcing structures ( 4 ) disposed in coaxial relationship with a geometric rotation axis of the tyre at positions axially spaced apart from each other and each comprising at least one first circumferentially-inextensible annular anchoring insert ( 5   a ); a belt structure ( 6 ) applied to the carcass structure ( 2 ) at a radially external position thereof, a tread band ( 9 ) applied at a radially external position to the belt structure ( 6 ) and a pair of sidewalls ( 10 ) applied to the carcass structure ( 2 ) at laterally opposite positions. The self-supporting tyre further comprises at least at one elastic stiffening insert ( 11 ) arranged at least at one of said sidewalls ( 10 ) and having a radially internal end portion ( 15 ) disposed at least partly in axial side by side relationship against the first annular anchoring insert ( 5   a ).

The present invention relates to a self-supporting tyre for vehicle wheels, comprising: a carcass structure having at least one carcass ply with end flaps in engagement with respective annular reinforcing structures which are disposed in coaxial relationship with a geometric rotation axis of the tyre at positions axially spaced apart from each other and each comprising at least one first circumferentially-inextensible annular anchoring insert; a belt structure applied to the carcass structure at a radially external position thereof; a tread band applied to the belt structure at a radially external position of same; at least one pair of sidewalls applied at laterally opposite positions to the carcass structure; at least one elastic stiffening insert incorporated into the carcass structure at least at one of said sidewalls.

The present invention also relates to a method of manufacturing a self-supporting tyre for vehicle wheels, comprising the steps of: preparing a carcass structure having at least one carcass ply provided with end flaps in engagement with respective annular reinforcing structures disposed in coaxial relationship with a geometric rotation axis of the tyre at positions axially spaced apart from each other and each. comprising at least one first circumferentially-inextensible annular anchoring insert; applying a belt structure to the carcass structure at a radially external position thereof; applying a tread band to the belt structure at a radially external position of same; applying a pair of sidewalls at laterally opposite positions to the carcass structure; incorporating at least one elastic stiffening insert into the carcass structure, at least at one of said sidewalls.

Tyres for vehicle wheels essentially comprise a carcass structure made up of one or more carcass plies that, in the most classic solutions, have the respective inner circumferential edges turned up around inextensible annular inserts being part of annular reinforcing structures and placed at axially opposite positions in the regions usually identified as tyre “beads”.

Applied to the carcass ply or plies, at a radially external position, is a belt structure comprising one or more belt layers radially superposed in succession. A tread band of elastomer material is radially superposed on the belt structure. The outer sides of the carcass structure are also covered with respective sidewalls made of elastomer material as well.

It is to be pointed out that, to the aims of the present invention, by the term “elastomer material” it is intended a rubber blend in its entirety, that is the assembly made up of at least one base polymer suitably amalgamated with reinforcing fillers and/or process additives of various types.

To give the tyre self-support qualities, i.e. the capacity to ensure ride over short-medium distances in the absence of inflation pressure, due to a puncture for example, one or more stiffening inserts of elastomer material are known to be integrated into the carcass structure, close to the tyre sidewalls; said inserts are usually referred to as “lunettes” and they conveniently support the vehicle load when the usual inflating pressure of the tyre is lacking.

In this connection different manufacturing solutions have been proposed, aiming at giving the tyre the required self-support features, without impairing ride comfort when the tyre is inflated. These solutions are essentially diversified as regards both the physico-chemical features of the elastomers employed in making the elastic stiffening inserts, and the number of the inserts to be provided, as well as in terms of positioning of said inserts relative to the carcass ply or plies.

Examples of these solutions that however do not ensure satisfactory results, are known from documents EP 0385192, U.S. Pat. No. 3,954,131 and GB 2053815 showing self-supporting structures comprising one lunette alone placed at each sidewall and disposed internally of the carcass ply or plies.

Good results, particularly as regards the tyre self-supporting capacity under deflated conditions, are achieved by adopting manufacturing solutions in which at least one of the elastic stiffening inserts which are present at each sidewall, is enclosed between two carcass plies forming a sort of closed container around it, as disclosed in documents GB 2087805, EP 475258 and EP 542252, for example.

The Applicant has however perceived that placing the elastic stiffening inserts in a sort of closed container defined by the carcass plies turned up around the annular anchoring structures tends to increase stiffness of the tyre sidewall too much, not only with reference to its vertical flexibility, i.e. in connection with substantially radial stresses with respect to the rotation axis of the tyre, but also with reference to its torsional responsiveness, i.e. in connection with stresses directed tangentially of the circumferential extension of the tyre itself.

By adopting particular expedients, as described in documents EP 475258 and EP 542252 in the name of the same Applicant for example, the possibility of restricting within limits, the vertical stiffness of the sidewall under running conditions with an inflated tyre are achieved. On the other hand, these technical solutions tend to make the tyre structure more complicated and heavier and are not efficient for the purpose of limiting the torsional stiffness which, as found out by the Applicant, is one of the decisive factors in terms of ride comfort, particularly at medium/high speeds. In fact, the tyre capacity of absorbing impacts transmitted by potholes or other unevennesses present in a road surface depends on the torsional stiffness of the tyre.

In accordance with the present invention it has been found that in the field of self-supporting-tyre manufacture, unexpected advantages can be reached if the elastic stiffening inserts have flaps axially overlapping the inextensible annular inserts, to ensure better anchoring of the reinforcing element to the annular structures and, through it, to the mounting rim during use at zero pressure.

In particular, it is an object of the present invention to provide a novel self-supporting tyre characterized in that said elastic stiffening insert has a radially-internal end portion disposed at least partly in axial side by side relationship against said first annular anchoring insert.

It is a further object of the invention to provide a method of manufacturing a self-supporting tyre for vehicle wheels, characterized by the fact of disposing said at least one first annular anchoring insert at a position in side by side relationship against a radially-internal end portion of the elastic stiffening insert.

Further features and advantages will become more apparent from the detailed description of a preferred but not exclusive embodiment of a method of manufacturing a self-supporting tyre for vehicle wheels, and a self-supporting tyre obtainable by said method, in accordance with the present invention. This description will be set forth hereinafter with reference to the accompanying drawings given by way of non-limiting example in which:

FIG. 1 is a fragmentary and cut-away perspective view of a tyre built in accordance with the present invention, associated with a toroidal support;

FIG. 2 is a fragmentary perspective view of the application of an elastic stiffening insert and a first annular anchoring insert being part of an annular reinforcing structure, onto one of the sides of the toroidal support;

FIG. 3 is a fragmentary perspective view diagrammatically showing the sequence of lying down strip-like sections for the purpose of forming a first carcass ply of the tyre, a second annular anchoring insert and an auxiliary filling element in accordance with the invention;

FIG. 4 is a fragmentary perspective view diagrammatically showing the sequence of laying down strip-like sections, for the purpose of forming a second carcass ply of the tyre, and a third annular anchoring insert, in accordance with the invention;

FIG. 5 is a cross half-section of the tyre made in accordance with the preceding figures;

FIG. 6 shows a cross half-section of a second embodiment of a tyre in accordance with the present invention.

With reference to the drawings, a tyre for vehicle wheels provided with a carcass structure 2 and made following the method of the present invention has been generally identified by reference numeral 1.

In the embodiment shown in the drawings, the carcass structure 2 has a first and a second carcass plies 3 a, 3 b having a substantially toroidal conformation and in engagement, through their opposite end flaps, with a pair of annular reinforcing structures 4 (only one of which is shown in the drawings) disposed in coaxial relationship with a geometric rotation axis of the tyre at positions axially spaced apart from each other; each of the annular reinforcing structures 4, when the tyre is completed, is placed at the region usually identified as “bead” and comprises at least one annular anchoring insert 5 a, 5 b, 5 c, to ensure anchoring of the tyre 1 to a corresponding mounting rim.

Applied to the carcass structure 2, at a radially external position, is a belt structure 6 comprising one or more belt strips 7 a, 7 b and 8. Circumferentially superposed on the belt structure 6 is a tread band 9 in which, following a moulding operation carried out concurrently with the tyre vulcanization, longitudinal and transverse grooves 9 a are formed which are conveniently disposed to define a desired “tread pattern”.

Tyre 1 also comprises a pair of so-called “sidewalls” 10, laterally applied to the carcass structure 2 on opposite sides thereof and further incorporates at least one elastic stiffening insert 11, at least at one of said sidewalls 10.

The carcass structure 2 can be possibly coated with a so-called “liner” 12, essentially consisting of at least one air-tight layer 12 a of elastomer material adapted to ensure a hermetic seal of the tyre when inflated.

Assembling of the above listed components as well as manufacture of one or more of same takes place with the aid of a toroidal support 13, diagrammatically shown in FIG. 1, the shape of which matches the configuration of the inner walls of the tyre 1 to be made.

The toroidal support 13 may have sizes of a linear value preferably reduced by an amount included between 2% and 5%, as compared with those of the finished tyre and measured just as an indication along the circumferential extension of the support itself at an equatorial plane X-X thereof which is coincident with the equatorial plane of the tyre.

The toroidal support 13, neither described nor shown in detail because it is not of particular importance to the aims of the invention, may for example consist of a collapsible or dismountable drum, or of an inflatable bladder suitably strengthened to take and keep the desired toroidal conformation under inflated conditions.

All that being stated, manufacture of tyre 1 first involves formation of liner 12, if any.

This liner 12 can be advantageously made by circumferentially winding up around the toroidal support 13, at least one ribbon-like band 14 of air-tight elastomer material, produced from an extruder and/or a calender located close to the toroidal support itself. As viewed from FIG. 1, winding of the ribbon-like band 14 substantially takes place with formation of circumferential coils disposed consecutively in side by side relationship so as to follow the cross-section profile of the outer surface of the toroidal support 13.

To the aims of the present description by cross-section profile it is intended the configuration exhibited by the half-section of the toroidal support 13 sectioned in a plane radial to the geometric rotation axis of the toroidal support itself, not shown in the drawings, which is coincident with the geometric rotation axis of tyre 1 and, consequently, of the carcass structure 2 being manufactured.

In accordance with the present invention, the elastic stiffening support or supports 11 (only one of which is shown in the accompanying drawings) are directly formed on the toroidal support 13, each at an axially external position either against the side portions 14 a of the ribbon-like band 14 of air-tight elastomer material, if present, or otherwise directly against the side portions 13 a of the toroidal support 13. In more detail, as shown in the accompanying drawings, each elastic stiffening insert 11 preferably having a modulus of elasticity included between 30 MPa and 50 MPa has a cross-section profile substantially in the form of a lunette, gradually tapering towards a radially internal apex lla and a radially external apex 11 b thereof, placed just as an indication close to a shoulder region of the tyre.

Advantageously, each of the elastic stiffening inserts 11 can be made by winding at least one continuous strip of elastomer material into coils disposed in axial side by side relationship with, and/or superposed on each other, which strip is forced through an extruder operating close to the toroidal support 13.

The continuous strip may have the final conformation in section of the elastic stiffening insert 11, already on coming out of the respective extruder. However, the continuous strip should preferably have a smaller section than that of the elastic stiffening insert 11, the latter being obtained by applying the strip itself in the form of several coils disposed in side by side and/or superposed relationship, so as to define the insert 11 itself in its final configuration. For further details concerning accomplishment of each elastic stiffening insert 11 please refer to the description of document WO 0136185 and/or document WO 0035666, both in the name of the same Applicant.

After formation of the elastic stiffening inserts 11, at least one first annular anchoring insert 5 a being part of the above mentioned annular reinforcing structures 4 is applied onto the elastic stiffening insert 11.

The circumferentially-inextensible annular anchoring insert 5 a is substantially in the form of a circular crown concentric with the geometric rotation axis of the toroidal support 13 and has a radial size corresponding to at least twice its axial size. In addition, the annular anchoring insert 5 a is placed against a radially internal end portion 15 presented by the elastic stiffening insert 11 at the respective radially internal apex 11 a more specifically, the radially internal end portion 15 of the elastic stiffening insert 11 is at least partially disposed in axial side by side relationship against the annular anchoring insert 5 a.

In particular, in the embodiment shown in FIGS. 1 to 5, the first annular anchoring insert 5 a is placed at an axially external position against the end portion 15 of the elastic stiffening insert 11.

The first annular anchoring insert 5 a is preferably made up of at least one thread-like metal element helically wound up around the rotation axis of the tyre to form at least one series of radially superposed coils 16. Coils 16 can be defined by a continuous spiral or by concentric loops formed by respective strip-like elements.

When laying-down of the elastic stiffening insert 11 and the first annular anchoring insert 5 a is over, building of tyre 1 goes on with the step of applying the carcass ply or plies 3 a, 3 b by laying down, as better clarified in the following, strip-like sections which in the course of the present description will be distinguished between inner sections 17 and outer sections 18 respectively, depending on the placement they have within the carcass structure 2. The strip-like sections 17, 18 are advantageously obtained from at least one continuous strip-like element preferably having a width included between 3 mm and 15 mm, essentially made up of longitudinally-disposed thread-like elements of textile or metallic material at least partly incorporated into one or more layers of elastomer material.

Such a continuous strip-like element can be advantageously produced from a calender or extruder installed in the vicinity of the toroidal support 13 on which building of tyre 1 takes place, so that said element may be guided into a deposition apparatus adapted to sequentially cut it to form the strip-like sections 17, 18 concurrently with deposition of same onto the toroidal support itself.

In more detail, execution of the cutting operation on each strip-like section 17, 18 is immediately followed by deposition of said section onto the toroidal support 13 giving the strip-like section a U-shaped configuration around the cross-section profile of the toroidal support itself, in such a manner that in the strip-like section 17, 18 it is possible to identify two side portions 17 a, 18 a radially extending towards the axis of the toroidal support 13, at positions axially spaced apart from each other and axially external to the elastic stiffening insert 11, and one crown portion 17 b, 18 b extending at a radially external position between the side portions 17 a, 18 a.

Further details about the structural features and the manufacturing and positioning modalities concerning the continuous strip-like element and the strip-like sections 17, 18 are described in documents EP 928 680 and EP 928 702, in the name of the same Applicant, contents of which are considered as fully incorporated herein.

The toroidal support 13 can be driven in angular rotation in a stepping movement in synchronism with operation of said deposition apparatus, so that the cutting action of each strip-like section 17, 18 is followed by laying down of said section to a position circumferentially spaced apart from the previously laid down section 17, 18.

In more detail, rotation of the toroidal support 13 takes place according to angular movement steps or pitches to each of which corresponds a circumferential displacement that, depending on requirements, can be substantially equal to the width of each strip-like section 17, 18, or to a multiple of this width. Consequently, the strip-like sections 17, 18 will be laid down according to a circumferential distribution pitch substantially corresponding to their width, or a multiple of this measure. It should be pointed out to the aims of the present description that, if not otherwise stated, the term “circumferential” refers to a circumference-lying in the equatorial plane X-X and close to the outer surface of the toroidal support 13.

In particular, in the embodiments shown, the angular movements of the toroidal support 13 take place in a manner adapted to cause, by a first full revolution of the toroidal support itself around its own axis, laying down of the axially internal sections 17 circumferentially distributed according to a circumferential pitch equal to the width of each of them, so as to form the first inner carcass ply 3 a.

In addition, the axially internal strip-like sections are of such a length that the end flaps 19 of the side portions 17 a of such sections are axially superposed on the first annular anchoring insert 5 a.

If required, laying down of the axially internal strip-like sections 17 may take place in an inclined orientation with respect to the circumferential extension direction of the toroidal support, at an angle included between 15° and 35° for example.

Adjustment of the deposition angle of the strip-like sections can be for example obtained by suitably orienting the geometric rotation axis of the toroidal support relative to the deposition apparatus.

Subsequently to laying down of the axially internal sections 17, formation of the carcass structure 2 goes on by laying down of at least one second annular anchoring insert 5 b against the end flaps 19 of the axially internal sections 17 themselves.

The second annular anchoring insert 5 b is therefore disposed in axial side by side relationship with the first annular anchoring insert 5 a at an axially external position relative to the first carcass ply 3 a.

The end flaps 19 of the axially internal sections 17 therefore are axially interposed between the first annular anchoring insert 5 a and the second anchoring annular insert 5 b.

In accordance with a preferential solution, the second annular anchoring insert 5 b is directly built against the end flaps 19 of the strip-like sections 17, thereby forming coils 16 by winding up of the strip-like element possibly with the aid of rollers or other convenient means acting against the action of the surface of the toroidal support 13.

An auxiliary filling body 20 of elastomer material may be combined with the second annular anchoring insert 5 b, said filling body having a modulus of elasticity preferably greater than that of the stiffening insert 11, preferably included between 75 MPA and 95 MPA, and radially tapering from the second annular insert 5 b away from the geometric rotation axis of the toroidal support 13.

The auxiliary filling body 20 can be in turn directly applied against the first carcass ply 3 a in the same manner as pointed out with reference to formation of the elastic stiffening insert 11.

After application of the auxiliary filling body 20 of the annular reinforcing structures 4, formation of the carcass structure 2 goes on by laying down of the axially external sections 18 applied to the toroidal support 13 in the same manner as specified for the axially internal sections 17, so as to form a second carcass ply 3 b.

In a convenient embodiment, the axially external strip-like sections 18 are laid down in a crossed orientation with the inner sections 17, preferably at an angle symmetrically opposite to that shown by said inner sections, with reference to the circumferential-extension direction of the carcass structure 2.

Laying down of the axially external strip-like sections 18 preferably takes place with a circumferential pitch substantially corresponding to the width of said sections so as to complete formation of the second carcass ply 3 b following execution of a single complete revolution by the toroidal support 13 around its rotation axis.

According to an alternative embodiment not shown, the inner strip-like sections 17 are laid down, by a first complete revolution of the toroidal support 13 itself around its axis, with a pitch corresponding to a multiple of their width; the outer sections 18 are distributed with a circumferential pitch corresponding to a multiple of their width and each have the respective crown portion 18 b interposed in a circumferential side by side relationship between the crown portions 17 b of two axially internal sections 17, to define a single carcass ply 3 a, 3 b therewith.

The respective side portions 17 a, 18 a are axially offset from each other to house the second annular anchoring insert 5 b in the gaps between the side portions of the inner 17 a and outer 18 a sections.

Therefore, in both embodiments, when laying down is completed, the second annular anchoring insert 5 b is interposed between the end flaps 19 of the axially internal sections 17 and the end flaps 21 of the axially external sections 18.

The sections of the first and second series 17, 18 are mutually joined along the whole extension of the cross-section profile of the toroidal support itself except at the end flaps 19, 21 close to the beads.

In accordance with a preferential embodiment of the invention, after carrying out deposition of the axially external strip-like sections 18, formation of the annular reinforcing structures 4 is completed, by application of at least one third annular anchoring insert 5 c disposed in external side by side relationship with the end flaps 21 of the side portions 18 a of the axially external strip-like sections 18.

Preferably, each third annular insert 5 c is essentially made up of a wire or thread wound up into coils 16 disposed crownwise, in the same manner as described with reference to formation of the first annular insert 5 a and the second annular insert 5 b.

Following the above operation, each of the end flaps 21 of the axially external sections 18 is advantageously enclosed between the second 5 b and third 5 c annular anchoring inserts of the respective annular reinforcing structure 4.

In tyres of the radial type, usually applied to the carcass structure 2 is the belt structure 6.

Such a belt structure 6 can be made in any convenient manner envisaged by a person skilled in the art and, in the embodiment shown, it essentially comprises a first and a second belt strips 7 a, 7 b consisting of cords with a respectively crossed orientation. Superposed on the belt strips 7 a, 7 b is an auxiliary belt strip 8 which is for example obtained by arranging at least one continuous cord wound into substantially circumferential coils in axial side by side relationship around the belt strips themselves.

Advantageously, the belt structure 6 is at least partly superposed on a radially external portion 22 of the elastic stiffening insert 11 at its radially external apex 11 b, to establish the continuity between the two elements.

Then the tread band 9 is applied to the belt structure 6 while sidewalls 10 are applied to the side portions of the carcass structure 2, said sidewalls too being obtained in any manner convenient for a person skilled in the art.

Embodiments of a belt structure, sidewalls.and a tread band to be advantageously adopted for the complete building of tyre 1 on the toroidal support 13 are described in document EP 919 406, in the name of the same Applicant.

Tyre 1 thus built now lends itself to be submitted, possibly after removal of support 13, to a vulcanization step that can be conducted in any known and conventional manner.

An alternative example of a tyre with a self-supporting carcass structure 2 to be obtained in accordance with the present invention is shown in FIG. 6.

According to the embodiment shown in FIG. 6, laying down of the first annular anchoring insert 5 a is carried out before laying down of the elastic stiffening insert 11 directly against the side portions 13 a of the toroidal support 13, so that the first annular anchoring insert 5 a may keep an axially internal position against the end portion 15 of the elastic stiffening insert 11.

Accomplishment of each component takes place substantially in the same manner as previously described with reference to FIGS. 1 to 5 or in a similar way.

In an embodiment not shown, the elastic stiffening insert 11 may extend on both sides of the first annular anchoring insert 5 a to ensure the maximum contact surface between the two elements. The radially internal portion 15 of said elastic stiffening insert 11 therefore has a first end length placed at an axially internal position relative to the first annular anchoring insert 5 a and a second end length placed at an axially external position relative to the first annular anchoring insert 5 a. The first annular anchoring insert 5 a is therefore axially interposed between two end lengths belonging to the end portion 15 of the elastic reinforcing insert 11.

It should be noticed that each elastic stiffening insert 11, disposed internally of the carcass plies 3 a, 3 b and in contact relationship with the first inner ply 3 a along its axially external surface, can be made up of a plurality of axially-disposed contiguous layers formed with blends of different moduli of elasticity.

For example, as shown in the accompanying figures, the elastic stiffening insert 11 can be formed with two axially superposed layers 23 a, 23 b without interruption. The second axially-outermost layer 23 b mainly submitted to tensile stresses, is in direct contact with the carcass plies 3 a, 3 b and preferably has a modulus of elasticity greater than the modulus of elasticity of the first innermost-layer 23 a mainly submitted to compressive stresses.

The containment degree of the deformations of the elastic stiffening inserts 11 can therefore be modulated by modifying the construction scheme of the elastic stiffening inserts 11, depending on requirements, above all in connection with their position relative to the annular anchoring inserts 5 a, 5 b, 5 c, so as to give tyre 1 the desired self-support qualities without increasing the torsional rigidity and weight of same too much, which values are particularly important for ride comfort.

The direct connection between the stiffening insert and annular anchoring insert proposed by the invention ensures a greater structural continuity between the two elements and represents a net improvement over known solutions, in which the lunette is maintained separated from the bead ring due to interposition of at least the carcass plies turned up around said ring.

In fact, the anchoring scheme in accordance with the present invention under ride conditions with a deflated tyre, enables the tractive load due to deformation of the area immediately overlying the annular anchoring insert to be transferred to the inner ply with greater efficiency.

In addition, the anchoring scheme in accordance with the present invention enables a sufficient radial stiffness with a deflated tyre to be obtained even by adopting a single stiffening insert applied to the inside of the carcass plies, thus avoiding the complexity, heaviness and other functional problems typical of structures provided with several inserts.

Finally, the invention enables accomplishment of a self-supporting tyre the carcass structure of which lends itself to be directly obtained on a toroidal support on which the whole tyre can be advantageously built.

In this way, all problems connected with manufacture, storage and management of semifinished products which are common to manufacturing processes of a traditional conception are eliminated. 

1. A self-supporting tyre for vehicle wheels, comprising: a carcass structure (2) having at least one carcass ply (3 a, 3 b) provided with end flaps (19, 21) in engagement with respective annular reinforcing structures (4) disposed in coaxial relationship with a geometric rotation axis of the tyre at positions axially spaced apart from each other and each comprising at least one first circumferentially-inextensible annular anchoring insert (5 a); a belt structure (6) applied to the carcass structure (2) at a radially external position thereof; a tread band (9) applied at a radially external position to the belt structure (6); a pair of sidewalls (10) applied to the carcass structure (2) at radially opposite positions; at least one elastic stiffening insert (11) incorporated into the carcass structure (2), at least at one of said sidewalls (10); characterized in that said elastic stiffening insert (11) has a radially internal end portion (15) at least partly disposed in side by side relationship against said first annular anchoring insert (5 a).
 2. A tyre as claimed in claim 1, wherein the first annular anchoring insert (5 a) is placed at an axially external position against the end portion (15) of the elastic stiffening insert (11).
 3. A tyre as claimed in claim 1, wherein the first annular anchoring insert (5 a) is placed at an axially internal position against the end portion (15) of the elastic stiffening insert (11).
 4. A tyre as claimed in claim 1, wherein the radially internal portion (15) of said elastic stiffening insert (11) has a first end length placed at an axially internal position relative to the first annular anchoring insert (5 a) and a second end length placed at an axially external position relative to the first annular anchoring insert (5 a).
 5. A tyre as claimed in claim 1, wherein the elastic stiffening insert (11) is placed at an axially internal position relative to said at least one carcass ply (3 a, 3 b) and in contact relationship with said at least one carcass ply (3 a, 3 b).
 6. A tyre as claimed in claim 1, wherein the elastic stiffening insert (11) comprises at least one first axially-internal layer (23 a) and one second axially-external layer (23 b) superposed on the first layer (23 a) without interruption.
 7. A tyre as claimed in claim 6, wherein the first axially-internal layer (23 a) has a smaller modulus of elasticity than the second axially external layer (23 b).
 8. A tyre as claimed in claim 1, wherein said elastic stiffening insert (11) has a radially external portion (22) overlaid by said belt structure (6).
 9. A tyre as claimed in claim 1, wherein said first annular anchoring insert (5 a) comprises at least one thread-like element helically wound up around the rotation axis of the tyre to form at least one series of radially-superposed coils (16); said annular anchoring insert (5 a) having a radial size corresponding to twice its axial size.
 10. A tyre as claimed in claim 1, further comprising at least one second annular anchoring insert (5 b) disposed in axial side by side relationship with the first annular anchoring insert (5 a) and axially external to said at least one carcass ply (3 a, 3 b); said at least one carcass ply (3 a, 3 b) being axially interposed between the first annular anchoring insert (5 a) and the second annular anchoring insert (5 b).
 11. A tyre as claimed in claim 10, further comprising an auxiliary filling body (20) radially tapering from the second annular anchoring insert (5 b) away from the geometric rotation axis of the toroidal support (13).
 12. A tyre as claimed in claim 11, wherein the auxiliary filling body (20) has a modulus of elasticity greater than the modulus of elasticity of the elastic stiffening insert (11).
 13. A tyre as claimed in claim 1, wherein said at least one carcass ply (3 a, 3 b) comprises: strip-like sections (17, 18) circumferentially distributed around said rotation axis and each extending in a U-shaped configuration around the cross-section profile of the carcass structure (2), to define two side portions (17 a, 18 a) mutually spaced apart in an axial direction and a crown portion (17 b, 18 b) extending at a radially external position between the side portions (17 a, 18 a).
 14. A tyre as claimed in claim 13, wherein said strip-like sections (17, 18) comprise axially internal strip-like sections (17) and axially external strip-like sections (18); the side portions (17 a) of the axially internal sections (17) being axially offset with respect to the side portions (18 a) of the axially external sections (18), to house a second annular anchoring insert (5 b) in the gaps existing between said side portions (17 a, 18 a).
 15. A tyre as claimed in claim 14, wherein the axially internal sections (17) and axially external sections (18) are distributed with a circumferential pitch corresponding to the width of each section, to define a first carcass ply (3 a) and a second carcass ply (38 b) respectively, the latter being radially superposed on the first carcass ply (3 a) close to said crown portions (17 b, 18 b).
 16. A tyre as claimed in claim 14, wherein the axially internal sections (17) are distributed with a circumferential pitch corresponding to a multiple of their width, the axially external sections (18) are distributed with a circumferential pitch corresponding to a multiple of their width and each have the respective crown portion (18 b) interposed in circumferential side by side relationship between the crown portions (17 b) of two axially internal sections (17), to define a single carcass ply (3 a, 3 b) therewith.
 17. A tyre as claimed in claim 14, further comprising at least one third annular anchoring insert (5 c) disposed externally in side by side relationship against end flaps (21) of the side portions (18 a) of the axially external sections (18).
 18. A method of making a self-supporting tyre for vehicle wheels, comprising the steps of: preparing a carcass structure (2) having at least one carcass ply (3 a, 3 b) provided with end flaps (19, 21) in engagement with respective annular reinforcing structures (4) disposed in coaxial relationship with a geometric rotation axis of the tyre at positions axially spaced apart from each other and each comprising at least one first circumferentially-inextensible annular anchoring insert (5 a); applying a belt structure (6) to the carcass structure (2) at a radially external position thereof; applying a tread band (9) to the belt structure (6) at a radially external position thereof; applying a pair of sidewalls (10) to the carcass structure (2) at radially opposite positions; incorporating at least one elastic stiffening insert (11) into the carcass structure (2), at least at one of said sidewalls (10), characterized by arranging said at least one first annular anchoring insert (5 a) at a position in axial side by side relationship against a radially-internal end portion (15) of the elastic stiffening insert (11).
 19. A method as claimed in claim 18, comprising the steps of applying said at least one elastic stiffening insert (11) onto a toroidal support (13) at an axially external position against side portions (13 a) of said toroidal support (13); applying the first annular anchoring insert (5 a) to the elastic stiffening insert (11) at the radially-internal end portion (15) of said elastic stiffening insert (11).
 20. A method as claimed in claim 18, comprising the steps of applying the first annular anchoring insert (5 a) onto a toroidal support (13) at an axially-external position against side portions (13 a) of said toroidal support (13); applying the elastic stiffening insert (11) to the first annular anchoring insert (5 a) at the radially-internal internal portion (15) of said elastic stiffening insert (11).
 21. A method as claimed in claim 18, wherein the elastic stiffening insert (11) is obtained by winding at least one continuous strip of elastomer material into coils disposed in axial side by side relationship and/or radially superposed on each other.
 22. A method as claimed in claim 18, wherein preparation of the carcass ply (2) comprises the step of laying down circumferentially-distributed strip-like sections (17, 18) on a toroidal support (13), each of said sections (17, 18) extending in a U-shaped configuration around the cross-section profile of the toroidal support (13) to define two side portions (17 a, 18 a) mutually spaced apart in an axial direction, and a crown portion (17 b, 18 b) extending at a radially external position between the side portions (17 a, 18 a).
 23. A method as claimed in claim 22, wherein the strip-like like sections (17, 18) are laid down on said at least one first annular anchoring insert (5 a) and on said at least one elastic stiffening insert (11) previously deposited on the toroidal support (13).
 24. A method as claimed in claim 22, comprising the following steps: laying down axially-internal strip-like sections (17); applying at least one second annular anchoring insert (5 b) against end flaps (19) of the axially internal sections (17); laying down axially-external strip-like sections (18).
 25. A method as claimed in claim 24, wherein the axially internal sections (17) are distributed with a circumferential pitch substantially corresponding to their width to define a first carcass ply (3 a), and the axially external sections (18) are distributed with a circumferential pitch substantially corresponding to their width to define a second carcass ply (3 b) radially superposed on the first carcass ply (3 a) close to said crown portions (17 b, 18 b).
 26. A method as claimed in claim 24, wherein the axially internal sections (17) are laid down with a circumferential distribution pitch substantially corresponding to a multiple of their width, the axially external sections (18) are laid down with a circumferential distribution pitch substantially corresponding to a multiple of their width, each of them with the respective crown portion (18 b) interposed in circumferential side by side relationship between the crown portions (17 b) of two axially internal sections (17), to define a single carcass ply (3 a, 3 b) therewith.
 27. A method as claimed in claim 24, wherein before deposition of the axially external sections (18) a further step is carried out consisting in applying an auxiliary filling body (20) radially tapering from the second annular anchoring insert (5 b) away from the geometric rotation axis of the toroidal support (13).
 28. A method as claimed in claim 24, wherein after deposition of the axially external sections (18) the further step of applying at least one third annular anchoring insert (5 c) against end flaps (21) of said axially external sections (18) is carried out. 